JP5386858B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus such as an electrophotographic copying machine having a fixing device for fixing a toner image onto a recording medium, a printer, a FAX, and more specifically, an electromagnetic induction heating type fixing roller type fixing device. The present invention relates to an image forming apparatus.

An image output machine using an electrophotographic system is widely used, but in recent years, it is required to be ready for printing when it is desired to use it. In short, the return time from the standby state such as power-off or sleep to the start of the image forming operation is being shortened.
In order to shorten the recovery time, it is a condition that the fixing device needs to be in a printable temperature state, and the temperature rise time of the fixing device is being shortened. In order to shorten the fixing heating time, an IH method with high thermal efficiency is also adopted as a heating method. Further, in order to shorten the fixing temperature raising time, it is required to make the heat capacity of the pressure roller for contacting the fixing roller and the fixing roller to form the fixing nip as low as possible. As the IH fixing method, there are a method using a fixing belt and a method in which a heat generating layer is formed inside the fixing roller itself. The fixing belt system is based on a belt base material made of nickel electroforming or polyimide to ensure the strength of the fixing belt itself, so the heat capacity is slightly larger. There is an elastic member that also functions as a heat insulation on the top, and a heat generation layer and a surface release layer are provided on it, and the heat generation layer is heated by an external electromagnetic induction heating means. Can be obtained.

However, in the image forming apparatus, for shortening the start-up time for starting the image forming operation that are accelerating year by year, in the case of forming a color image, it is necessary to fix the toner of the four colors, fixing conditions the more the case of forming a monochrome image, thermally large energy formic is required. Furthermore, when the standing time of such long Tomokazu, fixing device is put it in any cooling condition, it is necessary to begin a job to the image formed from the cooled state, routine use and daytime It is a condition that a fixing defect is more likely to occur than when it is.
However, there is a demand for both a reduction in fixing start-up time and a high quality of the fixed toner image, and a longer life of the fixing device itself under any environment and image mode conditions. In particular, in a fixing device having a heat generating layer of an electromagnetic induction heating method in the fixing roller, the heat generating layer is a thin layer and the fixing roller itself needs to have elasticity, so that it is fixed by contact with the pressure roller. Since the heat generation layer is always bent at the nip portion, this bent shape may remain, and there is a problem in the durability of the heat generation layer or the fixing roller.
Further, if the fixing nip pressure is applied, the fixing roller itself is deformed, and there is a problem that gloss unevenness or defective fixing occurs at the deformed portion.
For this reason, in order to improve these problems, the fixing nip pressure is released except during use.

The other use is that to release the fixing nip pressure, techniques obtained by adding the pressure control in the fixing apparatus. In Patent Document 1, for a fixing device including a heat source inside a fixing roller, an optimal amount of heat can be selected for each mode by switching the fixing pressure depending on the paper size, paper type, and the number of sheets passed so far when the fixing temperature is reloaded. There is a statement that the power consumption during fixing is reduced. This optimizes fixing stability and power consumption by selecting the optimal fixing conditions (temperature, pressure) for each mode, but fixing when the environmental temperature is low or the power supply voltage is low. In addition to not being able to cope with the conditions where defects are likely to occur, it is necessary to wait for the temperature of the fixing roller and pressure roller to reach the target temperature in each mode. End up.
According to Patent Document 2, for a fixing device including a heat source inside the fixing roller, the fixing roller set temperature can be reduced by reducing the fixing pressure when there is no paper in the fixing device, and the standby consumption is reduced. There is a statement that power can be reduced and energy saving can be realized. Further, it is disclosed that energy saving in the low power mode is achieved by switching the fixing temperature in the low power mode according to the outside air temperature. However, this can achieve energy saving in the low power mode, but it is not able to cope with conditions where fixing failure is likely to occur such as when the environmental temperature is low or when the power supply voltage is low.
In Patent Document 3, in a fixing device having a fixing belt and a pressure belt, it is not possible to sufficiently fix a portion having a low toner height when pressure is applied by a roller over the belt, and glossiness unevenness occurs in a fixed image. There is a description that this phenomenon can be avoided by including a pressure control means for controlling the pressure applied to the fixing unit in accordance with the type of transfer paper in order to suppress the occurrence. However, this is intended to suppress gloss unevenness due to the type of paper by positively controlling the pressure, and is not intended to shorten the start-up and avoid fixing failure.
In Patent Document 4, when the temperature of the fixing roller is raised, the rotation speed of the fixing roller is made slower than that during normal printing, and the pressure roller is separated to suppress the outflow of heat from the fixing roller. It is disclosed that shortening is achieved. Patent Document 5 discloses that the pressure roller is separated when the temperature of the fixing is raised, thereby suppressing the outflow of heat from the fixing roller and shortening the temperature raising time of the fixing roller. However, this suppresses the heat flow to the pressure roller and shortens the start-up time. However, if the amount of heat stored in the pressure roller is small, the cold from the cooling state of the fixing device such as in the morning will be reduced. There is a risk of poor fixing at the start.

JP 2001-282041 A JP 2007-299010 A JP-A-2005-010593 JP 2002-31745 A JP 2005-326524 A

  As mentioned above, these conventional technologies shorten fixing start-up time and can be said to have its side effects.Fixing fixing while suppressing unnecessary extension of fixing start-up time even during cold start or constant temperature environment and low power supply voltage. It is difficult to prevent the occurrence of defects.

Therefore, the present invention has been made in view of the above problems, and the problem is that it is necessary to simultaneously reduce the time until the start of the image forming operation and stabilize the fixing quality including the morning one. Furthermore, it is an object to suppress the life deterioration of the fixing device. Furthermore, while represents short fixing at Tachinobo Riomi, it is an object to suppress the stabilization and deterioration of life of the fixing quality by pressurization control.

The features of the present invention, which is a means for solving the above problems, are listed below.
In the image forming apparatus of the present invention, a fixing device having a fixing member that fixes an unfixed image on a recording medium, and a pressure member that forms a fixing nip portion in contact with the fixing member and facing the fixing member with a predetermined pressure, An image comprising pressure control means for varying the contact pressure between the fixing member and the pressure member, a fixing temperature detecting means for measuring the surface temperature of the fixing member and the pressure member, and an environmental temperature detecting means for measuring the environmental temperature. forming apparatus odor Te, the fixing device includes a heating means for heating the fixing member, and a power supply means for supplying power to the heating means, and a power detecting means for detecting a power supply for supplying power, the power The detection means has a power supply means for supplying power to the electromagnetic induction heating means when it detects electric power below a predetermined value, and the power supply means has a power detection means for detecting the power supplied to the electromagnetic induction heating means. and, before Symbol pressure control means Can be set pressure of a plurality of stages, and, in until a print permission from when receiving a print job, the detection result of the detection by said fixing temperature detecting means, and the power for supplying power to said heating means When any of the detection results detected by the supply means is lower than the specified value, the applied pressure is higher than the standard applied pressure. When both of the detected results are lower than the specified value, the applied pressure is higher than the applied pressure 1. at a pressure 2, after the pressurization control before the recording medium sheet passing, during the sheet passing the record medium, characterized by higher than standard pressure the pressing force by the pressure control means.
The image forming apparatus of the present invention is further characterized in that after the recording medium is passed, the pressurizing control means sets the applied pressure to a standard applied pressure or lower than the standard applied pressure.
In the image forming apparatus of the present invention, the image forming operation is further started by detecting the surface temperatures of the fixing member and the pressure member.
The image forming apparatus according to the present invention is further characterized in that the pressure applied when the fixing member and the pressure member are determined to have good fixing conditions is used as a standard.
In the image forming apparatus of the present invention, further, it characterized by starting the image forming operation at a predetermined time after the print job operation starts.
Also, in the image forming apparatus of the present invention, further, the fixing member has, on a resilient body made of a sponge material, at least a heating layer made of a nonmagnetic material, laminating a release layer as a surface layer thereon It is characterized by.

  In the image forming apparatus according to the present invention, when it is determined that the fixing failure is likely to occur, the nip width is widened by increasing the pressure beyond the normal pressure, and a state in which the fixing stability is higher is temporarily formed and fixed. Defects can be avoided.

  The best mode for carrying out the present invention will be described below with reference to the drawings. Note that it is easy for a person skilled in the art to make other embodiments by changing or correcting the present invention within the scope of the claims, and these changes and modifications are included in the scope of the claims. The following description is an example of the best mode of the present invention, and does not limit the scope of the claims.

Hereinafter, an embodiment of an electrophotographic printer will be described as an image forming apparatus of the present invention.
First, the basic configuration of the printer according to the present invention will be described. FIG. 1 is a schematic configuration diagram showing an image forming apparatus according to the present invention.
The image forming apparatus 1 in FIG. 1 includes four process units 2 for yellow, cyan, magenta, and black (hereinafter referred to as Y, C, M, and K) as process units 2 that are toner image forming units. . These use different colors of Y, C, M, and K toners to form an image, but otherwise have the same configuration.
Taking the process unit 2 for generating a Y toner image as an example, this has a photoreceptor 20 and a developing device 50 as shown in FIG. The photosensitive member 20 and the developing device 50 are detachably attached to the image forming apparatus 1 main body.

FIG. 2 is a diagram showing an outline of a process unit as image forming means.
The process unit 2 includes a drum-shaped photoconductor 20 serving as a latent image carrier, a cleaning device 40 serving as a cleaning unit for the latent image carrier that removes and collects transfer residual toner attached to the photoconductor 20, and surface friction of the photoconductor 20. lubricant application blade 44 for uniformly coating a lubricant coating brush 43 and a lubricant to a coefficient to a predetermined value (zinc stearate) 45 on the photoconductor 20, for uniformly charging the photosensitive member 20 The charging device 30 is provided. A charging roller 31 included in the charging device 30 applies a charging bias obtained by superimposing a DC voltage on an AC voltage from a charging bias applying unit (not shown) to the surface of the photosensitive member 20 that is driven to rotate clockwise in the drawing by a driving unit (not shown). To charge uniformly. Subsequently, it exposed and scanned by a laser beam emitted from the exposure light 80 corresponding to an image signal to form an electrostatic latent image.

Developing device 50, a second developer accommodating portion 54a of the second conveying screw 53a is disposed, has a first developer accommodating portion 54b of the first feeding screw 53b is disposed, first development A toner concentration sensor 55 composed of a magnetic permeability sensor is installed on the lower surface of the agent container 54b , and the mixing ratio between the carrier particles, which are magnetic materials, and the toner is calculated from the magnetic permeability so as to obtain a predetermined toner concentration. The toner is supplied from the toner bottle 7 by a supply device (not shown). The first conveying screw 53b is rotationally driven by a driving means (not shown), and the developer in the first developer accommodating portion 54b is conveyed from the back side to the near side in the direction orthogonal to the drawing, and the first developer accommodating portion 54b. And enters the second developer accommodating portion 54a through a communication port (not shown) provided in the partition wall between the first developer accommodating portion 54a and the second developer accommodating portion 54a . Second conveyance screw over 53a in the second developer storage portion 54a, by being rotatably driven by a driving means not shown, is conveyed to the rear side of the developer from the in the foreground of the drawing. Above the second conveying screw over 53a, the developing sleeve 51 is disposed in the second conveying screw 53a and posture parallel, the developing sleeve 51 is rotated counterclockwise in FIG. Developing sleeve 51 is made of nonmagnetic material (Al Miniumu) pipes are roughened by sandblasting the surface. A magnet (not shown) is disposed inside the developing sleeve 51, and a part of the developer conveyed by the second conveying screw 53a is pumped up to the surface of the developing sleeve by the magnetic force generated by the magnet. Then, after the layer thickness is regulated by a doctor blade 52 arranged so as to maintain a predetermined gap from the developing sleeve 51, the layer thickness is regulated and conveyed to a developing region facing the photoconductor 20, from a developing bias applying means (not shown). A developing bias applied to the developing sleeve 51 causes toner to adhere to the electrostatic latent image formed on the photoconductor 20 to form a toner image. The developer that has consumed the toner by the development is returned to the second conveying screw 53 a as the developing sleeve 51 rotates. And if it conveys to the innermost end in a figure, it will return in the 1st developer accommodating part 54b through the communicating port which is not shown in figure.

The detection result of the magnetic permeability of the developer by the toner concentration sensor 55 is sent to a control unit (not shown) as a voltage signal. Since the magnetic permeability of the developer shows a correlation with the toner concentration of the developer, the toner concentration sensor 55 outputs a voltage having a value corresponding to the toner concentration. A control unit (not shown) includes information storage means such as a RAM, in which Vref, which is a target value of the output voltage from the toner density sensor 55, is stored. Vref is compared, a toner amount corresponding to the comparison result is supplied from a toner supply device (not shown), and toner is replenished from the back side of the first developer accommodating portion 54b in the developing device 50, and the toner concentration in the developer is set to a desired value. Keep the value of. This control by the toner density sensor 55 and the toner supply device is performed for each color individually.
An exposure device 80 is disposed below the process unit 2 in the drawing. The exposure device 80 serving as a latent image writing unit irradiates the surface of the photosensitive member of each process unit 2 with laser light based on the image information. Thereby, an electrostatic latent image is formed on the photoconductor 20. The exposure device 80 scans laser light emitted from a laser diode as a light source by a polygon mirror that is rotationally driven by a motor, and irradiates the photosensitive member through a plurality of optical lenses and mirrors. Instead of such a configuration , exposure means using an LED array may be employed.

Below the exposure device 80, a first paper cassette, the second paper cassette is disposed so as to overlap in the vertical direction. Within these paper feeding cassettes 91, respectively, are recorded medium serving recording paper housed in the top of the recording paper, the first paper feed row La, the second sheet feeding rows La respectively contact . When the paper feeding roller 92 is rotated counterclockwise at a predetermined timing by a driving means (not shown), the recording paper is arranged to extend in the vertical direction on the right side of the paper feeding cassette 91 in the drawing. Ejected toward the paper feed path. A plurality of conveyance roller pairs are disposed in the paper feed path, and the recording paper sent to the paper feed path is conveyed upward by these conveyance rollers 93.
A registration roller 94 is disposed in the paper feed path. When the recording paper is sent from the transport roller 93 immediately before the registration roller 94, the recording paper is temporarily stopped. Then, the registration roller 94 is driven at a predetermined timing in accordance with the timing at which the toner image formed on the intermediate transfer belt 72 reaches the nip formed between the secondary transfer roller 73 and the recording paper is Sends out toward the secondary transfer nip.

In the upper part of each process unit 2 in the figure, a transfer device 70 is provided that endlessly moves counterclockwise in the figure while stretching an intermediate transfer belt 72 that is a surface endless moving body. In addition to the intermediate transfer belt 72, the transfer device 70 serving as a transfer means includes a belt cleaning device 74, a primary transfer roller 71 disposed at a position where the photosensitive members 20 of the respective colors face each other, and an intermediate transfer belt 72 that receives external driving. A driving roller 75 to be driven, a belt tension roller 76, and the like are included. The drive roller 75 also serves as a counter roller for the secondary transfer roller 73.
While being stretched around these drive rollers 75, etc., they are moved endlessly in the counterclockwise direction in the figure by the rotational drive of the drive rollers 75.
The primary transfer roller 71 is in contact with the photoconductor 20 with the intermediate transfer belt 72 interposed therebetween, and forms a nip portion formed between the primary transfer roller 71 and the primary transfer roller 71. The toner image on the photoconductor 20 is transferred onto the intermediate transfer belt 72 by applying a transfer bias having a polarity opposite to that of the toner image formed on the photoconductor 20 to the primary transfer roller 71. The toner images of the respective colors formed by the process units 2 of the respective colors are sequentially primary transferred onto the intermediate transfer belt 72 to form a color image on the intermediate transfer belt 72.

The secondary transfer roller is disposed outside the intermediate transfer belt at a position facing the secondary transfer counter roller, which is a driving roller, across the belt, and is applied to the secondary transfer counter roller with a predetermined load by a spring load. In contact therewith, a secondary transfer nip is formed.
The color image formed on the intermediate transfer belt is moved to the secondary transfer nip by the rotational drive of the intermediate transfer belt, and at the same time, the recording paper is secondary transferred in synchronization with the toner image entering the secondary transfer nip. Enter the nip.
The toner image is secondarily transferred onto the recording sheet by a secondary transfer electric field and a nip pressure formed between the secondary transfer roller and the secondary transfer counter roller. The electric field for secondary transfer is formed by applying a transfer bias having the same polarity as the toner to the secondary transfer counter roller and grounding the secondary transfer roller.
On the intermediate transfer belt after passing through the secondary transfer nip, a small amount of toner that has not been transferred to the recording paper remains and adheres. This is cleaned by a belt cleaning unit. In the belt cleaning unit, the cleaning blade is brought into contact with the surface of the intermediate transfer belt, whereby the transfer residual toner on the belt is scraped and removed.
The transfer residual toner removed from the intermediate transfer belt is accommodated in a waste toner bottle and discarded.

A fixing device 10 is disposed above the secondary transfer nip portion. The fixing device 10 includes a fixing roller 11 that includes an electromagnetic induction heat generating layer, a pressure roller 12 that is in contact with the fixing roller 11 with a predetermined pressure to form a predetermined nip width, a temperature sensor (not shown), and the like. . On the left side of the fixing roller 11 in the figure, there is an IH coil unit 13 that is an electromagnetic induction means for generating heat in the electromagnetic induction heating layer in the fixing roller 11. The fixing roller 11 is heated by electromagnetic induction by the coil 132. In the fixing roller 11 and the like, the pressure roller 12 rotates clockwise and the fixing roller 11 rotates counterclockwise by a driving source (not shown).
The recording paper that has passed through the secondary transfer nip is separated from the intermediate transfer belt 72 and then fed into the fixing device 10. Then, in the process of being conveyed from the lower side to the upper side in the figure while being sandwiched by the fixing nip portion of the fixing device 10, the toner image is heated on the fixing roller 11 and simultaneously pressed by the fixing nip portion, so that the toner image is formed on the recording paper. It can be fixed.
The recording paper subjected to the fixing process in this way is discharged out of the apparatus via the paper discharge roller 95 and is stacked on the upper surface of the printer main body.
Above the transfer unit, toner bottles 7 of respective colors that contain Y, C, M, and K toners are disposed. The toner of each color stored in the toner bottle 7 is appropriately supplied to the developing device 50 of the process unit 2 of each color. These toner bottles 7 can be detached from the main body of the image forming apparatus 1, and the toner bottle 7 can be replaced when the toner remaining in the bottle is exhausted.

Next, the fixing device will be described in detail. FIG. 3 is a cross-sectional view illustrating a configuration of main members of the fixing device. FIG. 4 is a cross-sectional view illustrating an internal configuration of the fixing roller.
The main components of the fixing device, the electromagnetic induction heating unit as a magnetic flux generating means (the IH coil) 13, the fixing roller 11, pressure roller 12 and the like are exemplified up.
Here, the fixing roller 11 which is a fixing member functioning as a heat generating member is a core metal 111 made of a nonmagnetic material such as SUS304, the surface of the core metal gives elasticity to the roller itself, and further has a heat resistance functioning as a heat insulating member. Sponge elastic layer 112, heat generating layer 113 (consisting of a first nonmagnetic material layer 113a made of a first nonmagnetic material and a second nonmagnetic material layer 113b made of a second nonmagnetic material), an antioxidant layer 114, a surface A release layer 115 is laminated.
The elastic layer 112 is made of an elastic material such as a silicone rubber foam and occupies most of the roller configuration. Due to this heat insulating action, the heat capacity is not so large, and a good fixed image can be obtained. As the first nonmagnetic material, SUS304, SUS301, SUS316 (all of which are nonmagnetic stainless steel) or the like as a nonmagnetic material can be used. As the second nonmagnetic material, copper (Cu) or the like as the nonmagnetic material can be used. The volume resistivity of the second nonmagnetic material is about 1.7 × 10 ⁻⁸ Ω · m, which is smaller than the volume resistivity of the first nonmagnetic material. As the second nonmagnetic material, silver (Ag), aluminum (Al), or the like is used. The heat generating layer 113 made of the first nonmagnetic material and the second nonmagnetic material generates eddy currents by the magnetic flux generated from the induction heating unit 13 and is electromagnetically heated.
The antioxidant layer 114 is made of nickel (Ni) and has a thickness of 5 μm or less. The antioxidant layer 114 is for preventing oxidation of the second nonmagnetic material made of copper.
The outermost release layer 115 is made of a fluorine compound such as PFA and has a thickness of 30 μm. The release layer 115 is for improving the toner release property on the surface of the fixing roller 11 in direct contact with the toner image. As described above, each layer (core metal 111, elastic layer 112, heat generating layer 113, antioxidant layer 114, release layer 115) made of different materials in the fixing roller 11 has a thickness in the width direction (of the recording medium). It is formed so as to be substantially constant over a direction orthogonal to the transport direction. Accordingly, the thickness of the fixing roller 11 (the total thickness of each layer) is also substantially constant in the width direction. In this way, by making the layer thickness of each layer in the fixing roller 11 uniform in the width direction, the function of each layer in the fixing step acts equally in the width direction.
The pressure roller 12 is formed by forming an elastic layer such as fluorine rubber or silicone rubber on a metal shaft core. The elastic layer of the pressure roller 12 is formed to have a thickness of 0.5 to 2 mm and an Asker C hardness of 60 to 90 degrees. The surface of the pressure roller 12 is also formed of a fluorine compound such as PFA in order to improve toner releasability. The pressure roller 12 is in pressure contact with the fixing roller 11 and forms a nip portion (fixing nip portion) in contact between the fixing roller 11 and the pressure roller 12 to fix and record the toner image. The medium is conveyed.
Further, the pressure roller 12 may be provided with a heat source such as an infrared lamp or a halogen lamp at the center of the shaft to directly control the temperature of the pressure roller 12. As a result, the temperature control of the fixing device 10 can be facilitated, and the occurrence of dirt such as offset can be suppressed and high-quality image quality can be obtained in a short time.

The fixing roller 11 is more elastic than the pressure roller 12 as a whole although the Asker C hardness of the fixing roller 11 itself is difficult to measure because the elasticity of the elastic layer 112 itself is affected by the heat generating layer 113 and the like. In the fixing nip portion, the deformation amount of the fixing roller 11 is larger than that of the pressure roller 12. Since the shape of the nip portion forms an arc on the pressure roller 12 side, when the recording medium is discharged from the fixing nip, the curvature of the nip outlet on the fixing roller 11 side is increased and the paper separation property is increased.
Further, when the heat generation layer 113 by thin electromagnetic induction heating is laminated on the elastic layer 112 and the release layer 115 is laminated thereon, the heat generation layer 113 is deformed in the fixing nip portion. Usually, in order to secure the fixing nip width and the paper separation from the fixing roller 11, the pressure roller 12 side is set to a high hardness, and the fixing nip shape is formed to draw an arc on the pressure roller 12 side. Let That is, the amount of deformation on the fixing roller 11 side is increased, and permanent deformation of the fixing roller 11 or pressure is applied to the adhesion portion of the heat generating layer 113 which is a thin layer, which may cause deterioration in durability. When the fixing device 10 is not in use, the fixing pressure may be released to suppress permanent distortion. However, excessive pressure should be avoided as much as possible even during paper feeding, resulting in poor fixing. Durability deterioration can be suppressed by applying pressure only under easy conditions.
The induction heating unit 13 includes a coil unit (excitation coil) 132, a core unit (excitation coil core) 131, a coil guide 133, and the like. The coil portion 132 is a coil portion 133 wound around a coil guide 133 disposed so as to cover a part of the outer periphery of the fixing roller 11 and wound in a width direction (perpendicular to the paper surface in the drawing). It is. The coil guide 133 is made of a heat-resistant resin material or the like and holds the coil portion 132. The core part 131 is made of a ferromagnetic material such as ferrite (relative permeability is about 1000 to 3000).
Although not shown, a thermistor is in contact with the surfaces of the fixing roller 11 and the pressure roller 12. The thermistor is a temperature sensitive element having high thermal response and detects the temperature of the surface of the fixing roller 11 and the pressure roller 12. Then, to adjust the amount of heating by the induction heating unit 13 have groups Dzu the detection result by the thermistor.
Although not shown, as the fixing device 10 used in the image forming apparatus of the present invention, the induction heating unit 13 including the coil unit 132 is disposed on the heating roller that stretches the fixing belt, and the fixing belt is heated. It may be used to fix the toner image. Further, a fixing belt provided with a metal layer capable of generating heat may be used as the heat generating rotating body.

The fixing device configured as described above operates as follows.
When the fixing roller 11 is driven to rotate in the clockwise direction in the drawing by a drive motor (not shown), the pressure roller 12 also rotates counterclockwise. The fixing roller 11 and the pressure roller 12 are connected by a gear, and a driving force is transmitted to each roller. The fixing roller 11 as a fixing member is heated by the magnetic flux generated from the induction heating unit 13 at a position facing the induction heating unit 13. Specifically, by supplying a high-frequency alternating current of 10 kHz to 1 MHz (preferably 20 kHz to 800 kHz) from the power supply unit (not shown) to the coil unit 132, an eddy current is generated in the heat generation layer 113 of the fixing roller 11. Joule heat is generated by the electric resistance and induction heating is performed. In this way, the fixing roller 11 is heated by induction heating of its own heat generating layer 113. Here become a point, generates heat by the fixing roller 11 near the surface, the elastic layer since it has a heat insulating effect, heat energy formic generated to heat the fixing roller 11 surface to minimize heat loss. As a result, quick temperature rise characteristics can be obtained. Thereafter, the surface of the fixing roller 11 heated by the induction heating unit 13 reaches the contact portion with the pressure roller 12 and heats and melts the toner image on the conveyed recording medium. More specifically, a recording medium carrying a toner image through the image forming process described above is fed between the fixing roller 11 and the pressure roller 12 while being guided by the fixing entrance guide plate 14, and from the fixing roller 11. The toner image is fixed to the recording medium by the heat received and the pressure received from the pressure roller 12, and the recording medium is sent out between the fixing roller 11 and the pressure roller 12 (fixing nip portion). The surface of the fixing roller 11 that has passed through the fixing position then reaches the position facing the induction heating unit 13 again and is reheated. Such a series of operations is continuously repeated to complete the fixing step in the image forming process.

Next, a pressure control mechanism of the pressure roller 12 with respect to the fixing roller 11 will be described.
FIG. 5 is a diagram illustrating a pressure control mechanism that presses the pressure roller against the fixing roller. FIG. 5 shows an example of the pressurization control mechanism, and the present invention is not limited to this embodiment.
The image forming apparatus 1 of the present invention includes a pressure control unit 18 that varies the contact pressure between the fixing roller 11 and the pressure roller 12 as shown in FIG. The pressure control means 18 includes an arm 15, a pressure control cam 16, and a pressure spring 17 . Both ends of the pressure roller 12 are rotatably supported by bearings, and are pressed against the fixing roller 11 by the spring pressure of the pressure spring 17 via the arm 15. The fixing nip width at this time is about 8 to 10 mm.
The spring pressure can be obtained in a pressurized state and a depressurized state by rotation by the pressurization control cam 16. Further, depending on the cam shape of the cam 16, the pressing force, that is, the fixing nip width can be controlled to be at least a plurality of pressing forces. Cam 16 is rotated in stepping Spider over data not shown, it is possible to vary the pressure by stopping at any given position of 3 to such, position 0 (b), the thus, the cam 16 Pressurization is controlled at the position. Pressure spring 17 and the cam 16 and the pressure control mechanism 18 consisting of the arm 15 is provided at both ends of the pressure roller 12, the cam 16 at both ends to rotate in phase, the stepping spider over data are connected by a shaft The drive is getting at the same time.
In addition, the pressure switching means supported by the rotating shaft is rotated by a predetermined amount, and the pressing force of the pressure roller 12 to the fixing roller 11 can be switched in a stepless manner by switching the side surface facing the pressure lever. can do. By providing many positions, it is possible to perform more accurate fixing control.

Further, in the image forming apparatus 1 of the present invention, at least one selected from the group consisting of the fixing roller 11, the pressure roller 12, and the environmental temperature from when a print job is received until when printing is permitted. From the above, it is determined whether or not the fixing condition is likely to occur. Here, the print job means that an image condition to be printed for printing, copying, etc. is set and an image forming operation is input to the main body of the image forming apparatus 1, and the image forming apparatus forms an image. It does not mean that the operation has started. Printing permission means that the main body of the image forming apparatus 1 is in a state in which an image forming operation is possible. The start of the image forming operation means starting a series of operations such as a charging process, an exposure process, a developing process, and a fixing process for forming an image for printing or the like. Whether the print job has been received is the first print job with the main switch turned on, for example, the first job from the room temperature in the morning, or a continuous print job continues. Does not consider whether is warmed to some extent.
That is, in the conventional image forming apparatus 1, after a print job is input, the fixing roller 11 and the pressure roller 12 in the fixing device 10 have a fixing defect that can fix the toner image on the recording medium with a predetermined strength. When it is determined that the condition for not performing has been reached, the image forming operation is started. However, in the image forming apparatus 1 of the present invention, the environmental temperature in which the fixing roller 11, the pressure roller 12, and the image forming apparatus 1 are placed is detected from when the print job is received until when the printing is permitted. It is determined whether at least one selected from the group consisting of the temperature sensors 4 is in a condition where fixing failure is likely to occur. Even in such a state, the image forming apparatus 1 of the present invention starts an image forming operation. For example, if image formation is performed regardless of the temperature reached by the fixing roller 11 or the like, fixing failure may occur. Therefore, in the image forming apparatus 1 of the present invention, the image forming operation is started even when it is determined that the fixing failure is likely to occur, and when the recording medium passes through the fixing device 10 at that time. The pressure is set higher than the standard pressure.

Here, one embodiment showing the control of the image forming apparatus of the present invention is shown. FIG. 6 is a flowchart showing the control of the image forming apparatus of the present invention.
After starting the print job (step S1), heating of the fixing roller 11 and the like is started (step S2). Thereafter, in FIG. 6, it is determined whether the temperature of the fixing roller 11 has reached a predetermined desired temperature (step S3). In FIG. 6, the desired temperature of the fixing roller 11 is set to 180 ° C. If the fixing roller 11 has reached 180 ° C., it is next determined whether or not the temperature of the pressure roller 12 has reached a desired temperature (step S4). The desired temperature in this case is 60 ° C. When the fixing roller 11 and the pressure roller 12 reach a desired temperature, the fixing control 11 is not in a condition where a fixing defect is likely to occur. (Step S5), the image forming operation is started (Step S6). The timing for applying the pressure may be any time from when it is determined that the pressure is applied until the recording paper or the like enters the fixing nip, and the timing is not particularly limited. The pressure applied by the pressure roller 12 to the fixing roller 11 in the fixing device 10 under such conditions is set as a standard pressure.
However, in the image forming apparatus 1 of the present invention, even when the fixing roller 11 or the like has not reached the desired temperature (step S3), it is further determined whether or not the desired time has been reached (step S7). Here, a description will be given using the fixing roller 11. Even if the pressure roller 12 and the environmental temperature are determined first, the same processing can be performed. In this case, when the desired time has been reached, the image forming operation is started without determining other conditions. In this case, even if the fixing roller 11 does not reach the predetermined temperature, the fixing roller 11 is heated for at least a predetermined time, and the temperature is accumulated until the sheet passes after the image forming operation starts. In consideration, further, in this case, the image forming operation is started while changing the conditions of the fixing device 10. The conditions of the fixing device 10 indicate, as an example, the fixing nip width and the applied pressure at the fixing nip portion. On the other hand, if the desired time has not been reached, the temperature of the fixing roller 11 is determined again (step S3). Note that the step of determining the predetermined time may be further provided after determining the environmental temperature after determining the fixing roller 12 and then determining the supply power.

In this case, the pressurizing force at position 1 is the pressurizing force in the standard state. With the start of this image forming operation, recording paper or the like is passed under a standard pressure. After passing the paper, leave it at the standard pressure or leave it out. By not applying pressure between the fixing roller 11 and the pressure roller 12, the fixing roller 11 can be prevented from being deformed, and the fixing device 10 can be used over a long period of time. In other words, if it is determined that the condition is likely to cause a fixing failure, the fixing nip is widened by raising it from the standard pressure, and a state with higher fixing stability is temporarily formed to avoid fixing failure. To do. On the other hand, under conditions where fixing defects are difficult to occur, standard stress and fixing nip width conditions are used, and unnecessary stress on the fixing roller 11 is minimized, and the life of the fixing roller 11 is deteriorated. Suppress. When the applied pressure is always high (the nip width is always wide), the deformation amount of the fixing roller 11 and the pressure roller 12 becomes large. Therefore, each member is wrinkled in shape when not driven, and the deformation amount is also large when driven. Therefore, member deterioration (elastic deterioration of the elastic body 112 and breakage of the bonded portion of the heat generating layer 113) is promoted. Since the start-up time of the fixing time follows normal judgment without unnecessarily extending the temperature-raising time under conditions where fixing defects are likely to occur, a stable start-up time can always be realized. Actually, fixing failure is likely to occur when the environmental temperature is low or the power supply voltage is low, but the influence of these disturbances can be eliminated by temporarily securing the necessary nip width.
This applied pressure is returned to a state in which the applied pressure is not applied after the print job is completed. The return time is after the end of the print job, but is not particularly limited to this, and may be immediately after the recording paper exits the fixing nip portion. However, for example, when the print job is continuous and the time between the recording sheets is short, it may be after the continuous print job. Conversely, when the time between print jobs is longer than the time required for the operation of changing the pressure, the pressure may be released to return to a state where no pressure is applied.

Next, it is determined whether the temperature of the pressure roller 12 has reached a desired temperature (step S4). If not, the environmental temperature is determined by the temperature sensor 4 (step S8). The desired temperature in this case is 17 ° C. Since the fixing roller 11 has not reached the desired temperature, if the environmental temperature is equal to or lower than the predetermined temperature (step S8), then the power supplied to the image forming apparatus 1 is determined (step S9). ). If the power is 92% or less of the predetermined desired power, it is a condition that a fixing failure is likely to occur. In this case, in order to maximize the pressure, the position of the cam 16 is set to position 3 (step S10), an image forming operation is started (step S11). The timing for applying the pressure may be any time from when it is determined that the pressure is applied until the recording paper or the like enters the fixing nip, and the timing is not particularly limited.
Also, in this case, if the power exceeds 92% of the predetermined desired power, the fixing failure is more likely to occur. In this case, the cam 16 is set to position 2 (step S12), and the image forming operation is started (step S13).
By directly knowing the environmental temperature, it is possible to predict that the condition is likely to cause a fixing failure. When the temperature is low, it is normal to raise the fixing roller 11 to a predetermined temperature until a fixing failure does not occur even in a low temperature environment. However, in the present invention, fixing failure can be avoided by increasing the pressing force and the nip width of fixing when the sheet is passed.
Further, in the electromagnetic induction heating fixing method (hereinafter simply referred to as “IH”), when the power supplied to the IH coil is low, a predetermined fixing temperature increase rate cannot be obtained, and the fixing process is completed. Become slow. Further, even when the paper is passed, if the supplied power is low, the amount of heat becomes insufficient, and the fixing temperature drops greatly, which may lead to fixing failure. By detecting such a condition, it is possible to maintain the fixing property by increasing the fixing pressure and increasing the fixing nip width. Normally, when the power is low, the heat-up time is extended to secure the amount of heat stored in the fixing, but by increasing the pressure in the condition judgment, the heat-up time is not unnecessarily extended. Fixability can be secured.
With the start of this image forming operation, recording paper or the like is passed under a pressure higher than the standard pressure. After passing the paper, return to the standard pressure or leave it under no pressure. By reducing the pressure between the fixing roller 11 and the pressure roller 12 or by not applying pressure, deformation of the fixing roller 11 can be prevented, and the fixing device 10 can be used over a long period of time. . Even when no pressure is applied, the fixing nip portion is formed with a constant width. The fixing roller 11 or the like has an elastic body 112, and the distance between the fixing roller 11 and the pressure roller 12 is designed to be smaller than the sum of the radii of both.
If the ambient temperature exceeds the predetermined temperature (step S8), then the power supplied to the image forming apparatus 1 is determined (step S14). If the electric power exceeds 92% of the predetermined desired electric power, the fixing condition is likely to occur, but the fixing condition is close to the standard. In this case, the position of the cam 16 is set to position 1. (Step S15), the image forming operation is started (Step S16). In this case, if the power is within 92% of a predetermined desired power, the cam 16 may be positioned between the position 3 and the position 1 under the condition that the fixing failure is likely to occur. In this case, the position of the cam 16 is set to position 2 (step S12), and the image forming operation is started (step S13). In this case as well, after the paper is passed, the pressure is returned to the standard pressure or no pressure is applied.

Accordingly, it is determined that a fixing failure is likely to occur, and the image forming operation is performed with the pressurization control unit 18 setting the pressure higher than the standard when the recording medium is fed during the image forming operation. Further, if the core metal 111 and the heat generating layer 113 of the fixing roller 11 are made of metal and are deformed while being kept at a high temperature, the deformed shape may remain due to creep deformation or the like, and the original shape may be removed even if the applied pressure is removed. It will not return to the shape. Therefore, the pressure is made lower than the standard after the recording medium is passed in the image forming operation. Therefore, the position of the cam 16 is set to position 0, and the applied pressure is reduced. However, the heating roller 11 and the pressure roller 12 are not separated from each other, and the elastic body 112 of the heating roller 11 is deformed so that the pressure is reduced and the fixing nip portion is formed. Deploy. As a result, deformation of the cored bar 111 and the heat generating layer 113 of the fixing roller 11 can be suppressed, and can be used stably over a long period of time.
In this embodiment, the first detected temperature at which the image forming operation is started is the fixing roller 11. However, in the present invention, the pressure roller 12 may be used. The pressure roller 12 and the fixing roller 11 are in contact with each other so as to form a fixing nip. Even if the temperature of the pressure roller 12 is first detected to determine the start of the image forming operation, the fixing roller 11 It can be easily predicted that the temperature has reached a desired temperature. Further, by controlling the pressure of the fixing device 10 in consideration of other conditions, a high-quality fixed image with no fixing failure can be obtained. be able to.
In the present invention, the first detected temperature at which the image forming operation is started may be the environmental temperature. The ambient temperature is detected from an outside air temperature from a temperature sensor 4 provided in the image forming apparatus 1. When the outside air temperature is very low, it takes time to reach the desired temperature even if the fixing roller 11 or the like is heated. However, it is often controlled at a normal temperature without considering that the outside air temperature is low under normal use standards. For this reason, if the temperature is normal, it is easy to predict the temperature reached by the fixing roller 11 and the like based on the heating time, and further, the pressing force of the fixing device 10 is controlled in consideration of other conditions. Therefore, it is possible to obtain a high-quality fixed image without fixing failure.

The image forming apparatus of the present invention will be described more specifically with reference to examples.
The image forming apparatus is a modified Imagio MPC4500 (manufactured by Ricoh), the printing speed is 40 sheets / minute (A4 horizontal feed) at full color output, and the process speed is 205 mm / s.
FIG. 7 is a flowchart showing the control of the embodiment of the present invention.
After the main power is turned on, heating of the fixing roller is started, and when the temperature of the fixing roller reaches 180 ° C., the recovery from the main power on (or the image forming apparatus is in the sleep state) is completed, The printer is ready for printing. If the image forming apparatus does not start the image forming operation as it is, the heating of the fixing roller is stopped, and the apparatus waits in a state where the halogen heater included in the pressure roller is turned on. Moreover, if you do not start the image forming operation as it apparatus turns off the halogen heater after 1 minute, the device itself is shifted to the sleep mode (energy saving mode).
When a print job is input, heating of the fixing roller is started, the fixing roller temperature reaches 180 ° C., and the image forming operation is started under the condition that the pressure roller temperature is 60 ° C. or higher. When printing plain paper, the fixing roller temperature is set to 160 ° C. By passing the paper, the fixing roller temperature is lowered by taking heat away from the fixing roller temperature of 180 ° C at the start of paper feeding. The paper is fed while heating the fixing roller so as to maintain a temperature of about 160 ° C.

At this time, in a state where the room temperature is higher than 17 ° C. or in a state where the power of the IH inverter is higher than 92%, there is little risk of fixing failure, and fixing control is performed by normal temperature control. When the room temperature is lower than 17 ° C. or when the power is 92% or less, when the fixing device is cooled (cold start), the heat storage of the fixing device itself even after the fixing roller temperature rises to a predetermined target temperature. for the amount is insufficient, fixing failure is likely to occur such as offset. Therefore, in general, when a condition where the room temperature is 17 ° C. or less or the power is 92% or less is detected, the sheet passing permission is allowed to store heat in the fixing device itself after the fixing roller temperature reaches a predetermined temperature. In the state where the fixing roller is maintained at 180 ° C., the fixing device is rotated idly and heat is stored in the fixing device. By entering this operation, cold offset can be prevented in advance, but waiting time increases. Depending on the conditions, it is necessary to idle for about 10 seconds at a room temperature of 17 ° C. or lower. If the idling is not performed, the image forming apparatus can complete the warm-up in 25 seconds. Therefore, if the idling is performed, the warm-up time is extended to about 35 seconds. In the morning in the winter, such an idling may occur every morning.

In this embodiment, this idling time can be avoided by pressurization control.
First, after the image forming apparatus is turned on, the pressure control cam is set to position 1 (standard printing state), heating of the fixing roller is started, and the temperature is raised to the target heating temperature of the fixing roller. An outside air temperature is detected from a temperature sensor provided in the image forming apparatus, and further, electric power is detected by an IH inverter. When the fixing roller temperature reaches 180 ° C., the fixing device completes the temperature rise and notifies the image forming apparatus main body that printing is ready. If the previously detected environmental temperature is higher than 17 ° C. and the IH inverter power is higher than 92%, the pressure control cam remains at position 1, and an immediate image forming operation starts when a print job is input. , Print. After that, when there is no print job, the pressure control cam is set to position 0 after 1 minute to release the fixing nip pressure (pressure release). During printing, if either the environmental temperature is 17 ° C or less or the IH inverter power is 92% or less is detected, when a print job is input, the pressure control cam is controlled to position 2 and the image is formed as it is. Perform the action.
If both the environmental temperature is 17 ° C. or lower and the IH inverter power is 92% during image formation, the pressure control cam is controlled to position 3 and printing is performed as it is.
At this time, the relationship between the pressure control cam position and the nip width is as follows.
The relationship between the pressure control cam position and the fixing nip state (fixing nip width) is a depressurized state at position 0, the fixing nip width is in the range of 0 to 5.0 mm, and at position 1, the fixing nip width is It is in the range of 8.5 to 9.5 mm. At position 2, the fixing nip width is in the range of 9.5 to 10.5 mm. At position 3, the fixing nip width is in the range of 10.5 to 11.5 mm. is there. As described above, the fixing nip width can be varied by pressure control under conditions where fixing failure is likely to occur, that is, in a state where the environmental temperature is low or the input power to the IH inverter is low. It is possible to ensure fixability without requiring an idling operation for heat storage.

The fixing failure is likely to occur when the first fixing device in the morning enters a print job from a cooled state. If the fixing device itself is warmed and stored by use of the fixing device, that is, if the pressure roller is sufficiently warmed, the fixing nip width may not be controlled by pressure control. In a state where the apparatus is continuously used, the pressure roller is in a high temperature state, so that the pressure control can be further adjusted by detecting the pressure roller temperature.
Specifically, when the pressure roller temperature is 60 ° C. or higher, the pressure control is controlled as follows.
That is, when the environmental condition A as the external condition is the environmental temperature ≦ 17 ° C., the fixing nip state (nip width) is set to position 1 (standard position), and the environmental condition B as the external condition is IH inverter power ≦ 92% In this case, the fixing nip state (nip width) is set to position 1 (standard position). If the environmental conditions are A and B, the position 2 is fixed.
As described above, by detecting the environmental temperature, the IH inverter power, and the pressure roller temperature and controlling the pressure to form the optimum fixing nip state, the waiting time like the heat storage operation is not generated. The image forming operation can be started within the normal print start-up time.

1 is a schematic configuration diagram illustrating an image forming apparatus according to the present invention. It is a figure which shows the outline of the process unit which is an image formation means. FIG. 3 is a cross-sectional view illustrating a configuration of main members of the fixing device. FIG. 3 is a cross-sectional view illustrating an internal configuration of a fixing roller. It is a figure which shows the pressure control mechanism which presses a pressure roller to a fixing roller. FIG. 3 is a flowchart showing control of the image forming apparatus of the present invention. It is one flowchart which shows control of the Example of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 2 Process unit 3 Adhesion amount sensor 4 Temperature sensor 7 Toner bottle 8 Waste toner bottle 10 Fixing apparatus 11 Fixing roller 111 Core metal 112 Elastic layer 113 Heat generation layer 113a First nonmagnetic material layer 113b Second nonmagnetic material layer DESCRIPTION OF SYMBOLS 114 Antioxidation layer 115 Surface layer 12 Pressure roller 121 Halogen heater 13 Electromagnetic induction heating part 131 Core part 132 Coil part 133 Coil guide 15 Arm 16 Pressurization control cam 17 Pressurization spring 18 Pressurization control means 20 Photoconductor 30 Charging device DESCRIPTION OF SYMBOLS 31 Charging roller 32 Charging roller cleaner 40 Cleaning device 41 Cleaning blade 42 Screw 43 Lubricant application brush 44 Lubricant application blade 45 Lubricant 50 Developing device 51 Developing sleeve 52 Doctor blade 53 Screw 53a Second conveyance Screw 53b First conveying screw 54 Developer accommodating portion 54a Second developer accommodating portion 54b First developer accommodating portion 55 Toner density sensor 70 Transfer device 71 Primary transfer roller 72 Intermediate transfer belt 73 Secondary transfer roller 74 Belt cleaning device 75 belt drive roller 76 Berutote emissions Deployment roller 80 exposure device 91 the paper feed cassette 92 sheet feed roller 93 conveying roller pair 94 registration rollers 95 discharge roller

Claims (6)

A fixing device having a fixing member that fixes an unfixed image on a recording medium, and a pressure member that forms a fixing nip portion in contact with the fixing member while facing the fixing member;
Pressure control means for varying the contact pressure between the fixing member and the pressure member;
Fixing temperature detecting means for measuring the surface temperature of the fixing member and the pressure member;
Te image forming apparatus odor and a environmental temperature detecting means for measuring the environmental temperature,
The fixing device includes a heating unit that heats the fixing member, a power supply unit that supplies power to the heating unit, and a power detection unit that detects supply power to supply power.
When the power detection means detects a predetermined power or less,
Power supply means for supplying power to the electromagnetic induction heating means;
The power supply means has power detection means for detecting power supplied to the electromagnetic induction heating means,
Prior Symbol image forming apparatus, the pressure control means are capable of setting the pressing pressure of the plurality of stages, and,
Either the detection result detected by the fixing temperature detection means or the detection result detected by the power supply means for supplying power to the heating means between when a print job is received and when printing is permitted If the pressure is lower than the value, the pressure 1 is higher than the standard pressure, and if both of the detection results are lower than the specified value, the pressure 2 is higher than the pressure 1 and the pressure is applied before passing the recording medium. After pressure control
When the sheet passing the record medium, the image forming apparatus characterized by higher than standard pressure the pressing force by the pressure control means. The image forming apparatus according to claim 1.
The image forming apparatus is characterized in that, after the recording medium is passed, the pressurizing control means sets the applied pressure to a standard applied pressure or lower than the standard applied pressure. The image forming apparatus according to claim 1, wherein
The image forming apparatus starts an image forming operation by detecting surface temperatures of a fixing member and a pressure member. The image forming apparatus according to any one of claims 1 to 3,
The image forming apparatus is characterized in that the pressure applied when it is determined that the fixing member and the pressure member are in good fixing conditions is a standard. The image forming apparatus according to claim 1,
The image forming apparatus further starts the image forming operation at a predetermined time after the start of the print job operation. The image forming apparatus according to claim 1,
The fixing member is
On the elastic body made of a sponge material, at least a heat generating layer made of a non-magnetic material,
An image forming apparatus comprising a release layer as a surface layer laminated thereon .

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